Highly wear-resistant zinc base alloy and method of making same



.Unitcd State P o 2,909,429 ,7 HIGHLY WEAR-RESISTANT ziNc BASE ALLOY ANDMETHOD OF MAKING SAME,

Robert F. Thomson, Grosse Pointe Woods, and James C. HolzwarthBirmingham, Mich., assignors to General Motors Corporation, Detroit,Mich.,,a corporation of Delaware 7 No Drawing. Application July 5, 1955Serial No. 520,149

16 Claims. c1. 75-178) 2,909,429 Patented Oct. 20, 1959 ICC zinc-richmelt in the form of a copper base intermediate ing kettle beingrequired. The uniform shrinkage characand a process forproducing such analloy. More particularly, the invention pertains to an alloy of thistype which is characterized by outstanding wear resistance propertiesdue to the presenceof hard particles of an iron-zirconiummanganesealloy. v i

Zinc base alloys "commercially used today for drawing dies-and similarpurposes usually possess inadequate wear properties for manyrequirements. it is therefore a principal objectof the present inventionto overcome this deficiency by providing a zinc base alloy characterizedby greatly increased .wear properties, high resistance to fracture,good, castability and homogeneity. his a further object ofthi'sinvention to provide a drawing. die formed of an inexpensive zincbase alloy which possesses high wear resistance, a low melting point.and uniform shrinkage. I v

, Theseand other objects and advantages are attained in accordancewith-the present invention with a zinc base alloy containing a smallamount of dispersed particles of iron-zirconium-manganese alloy. Theseparticles contain hard intermetallic compounds or phases ofmanganese-zirconium whichare primarily responsible for the outstandingwear resistance of the zinc base alloy; v

'In particular, we have found that a zinc base alloy which containssmall amounts of copper and aluminum,

as well 55.1116, aforementioned hard particles of ironzirconium-manganese, ,isfespeciallysuitable for use as a 3' drawing die.A small amount of magnesium also may be advantageously included in thealloy, In this type of zinc base alloy the and copper j are added toincrease the'tensile strength and hardness and to reduce thesolidification temperature of the alloy. Magnesium is 9 preferablyincludedin the alloy to overcomethe corrosive influence. of anyimpurities. which maybe present in the alloy. It tliere'fore .promotesdimensional stability and prevents a decrease in the strength of thealloy on aging.

The resultant material is a longfwearing, generally homogenous alloyhaving'good castability properties. 7

i 'As disclosed in co-pending patent application Serial No.l78,34'5,file'd August 8, 1950,,lin the name of James Q. Holzwarth, newPatent'No. 2,720,459, patented October 11,1955, the wear resistance of azinc base: alloy may be improved by the inclusion of dispersed, hardparticles .of nickel-titanium in the alloy. However,iron-zirconiumma'nganes'ealloys do not contain any relatively criticalnickel andhence'are preferred in theevent of a nickel shortage becauseof a national emergency or for other teristic of this alloy permits theexact size of castings to be predetermined with precision, eliminatingthe necessity for extensive use of profiling machines. Accordingly, thesubject alloy is ideally suited for use as a drawing die material sincethe processing of dies formed of this alloy is comparatively simple,requiring a minimum of equipment and labor. Cost is further reduced bythe fact that this alloy can be remelted many times, permitting thematerial in obsolete dies to be almost entirely recovered. 7

In addition, the facility with which this zinc base alloy can be castand the diversity of forms into which, the molten alloy will flow makeit a very desirable material for a variety of purposes. Furthermore,finished castings of'this alloy can be produced comparatively quickly,making them available for production use within a relatively short time.

The high Wear resistance of the final zinc base alloy is due to thepresence of the dispersed, hard particles ofironzirconium-manganesealloy in the softer matrix. These particlesdo not readily float orsettle 'out of the Zinc-rich melt since they have a specific gravitywhich closely approximates that of the melt, provided the iron contentis not excessive. Hence the present invention provides an alloy. whichhas proper particle distribution, as Well as optimum particle size,resulting in physical characteristics wlll ich satisfy all requirementsfor an outstanding tool a 0y.

Commercially satisfactory results may be obtained in accordance with ourinvention with a final zi-nc base alloy containing approximately 1% to3% by weight of hard particles of iron-zirconium-manganese alloy.However, the iron-zirconium-manganese particles maybe present in amountsas large as about 4% by ,weight, and in some instances a noticeableimprovement in Wear resistance results when these particles constituteas little as about 0.5% of the zinc base alloy. If the alloy containsmore than approximately 4% of these particles, the castability of thealloy is impaired audits cost becomes excessive. Hence, a desirable zincbase drawing die alloy which possesses exceptional wear resistance isone consisting essentially of about 2% to 5% aluminum, 0.5% to 5%copper, 1% to 3% hard particles of iron-zirconium-manganese and thebalance substantially all zinc. The inclusion of approximately v0.02% to0.3% magnesium'is beneficial to reduce the corrosive tendencies ofimpurities such as lead, cadmium and It will be understood, of course,that the zinc base alloy also may contain small amounts of silicon andother elements as incidental impurities.

Thus it can be seen that in accordance with our invention a zinc basealloy containing at least approximately zinc has its wear resistanceappreciably improved by the presence of the aforementioned hardiron-zirconiummanganese particles. It will be understood, however, thatthe term zinc base alloy, as used herein, is intended to encompass thosealloys in which zinc is the major constituent and preferably constitutesat least 50% of the alloy.

More specifically, we have obtained outstanding wear characteristics ina cast alloy consisting essentially of 87% to 93% zinc, 3% to 5%aluminum, 2% to 3.5% copper, 0.05% to 0.2% magnesium, and 1% to 3%ironzirconiuIn-manganese alloy in the form of dispersed hard particles,An alloy consisting of approximately 4% aluminum, 0.15% magnesium, 3.25%copper, 1.5% ironzirconium-manganese and the balance zinc plusincidental alloy.

impurities appears to possess optimum castability and wear resistanceproperties.

Wear resistance, of course, *is a function of both the size anddistribution of the hard iron-zirconium-manganese particles. Sinceparticle size and distribution are dependent on such factors as metalviscosity, solidification rates and methods of alloying, this inventionalso provides a preferred procedure for preparing the zinc base In thecase of a drawing die it is desirable to produce maximum wear resistancewithout causing scoring of the part being drawn.

The iron-zirconium-manganese alloy can be initially prepared by meltingtogether the three individual constituents- Commercially pure zirconiumand manganese may be conveniently employed. Theresultant pre-alloy alsomay contain small quantities of other metals, such as aluminum, silicon,chromium, magnesium and nickel. Normally the maximum amounts of theselatter metals would not exceed approximately 5% aluminum, 2% silicon, 1%chromium, 1% magnesium and 0.5% nickel. These exact percentages of theminor constituents are not critical in most instances, however, and arelisted as examples only.

Inasmuch as the iron-zirconium-manganese pre-alloy does not readilydissolve in the zinc-rich metal, it is preferred to introduce these hardparticles by means of an intermediate alloy or hardener containingcopper. When the iron-zirconium-manganese is added to molten copper, itis transformed substantially into the molten state. Duringsolidification of the intermediate alloy, there appears to be a decreasein the solubility of the iron-zirconiummanganese alloy in the copper,and this alloy is therefore preferentially isolated as a network in thecopper-rich matrix. In order to form long-wearing particles of suitablesize, this hardener is preferably added to the zinc in the solid state.Since it is desirable to cast the copper base intermediate alloy inshapes in which the copperrich matrix will dissolve most readily in themolten zincrich alloy, it is preferred to form castings having a highratio of surface area to volume, such as flat plates orthin sheets.Generally the formed iron-zirconium-manganese particles have diametersin the order of about 0.001 inch. If the particles are much smaller thanthis, the wear resistance of the final zinc base alloy is not increasedthe desired extent.

Upon introduction of the intermediate alloy to the zinc-rich melt, thecopper or copper-rich matrix is dissolved, leaving the relativelyinsoluble network of ironzirconium-manganese suspended in the zinc asWearresistant particles of appropriate size. Agitation of the zinc-richmelt causes these particles to become generally uniformly dispersedthrough the melt, and the particles remain so dispersed in thesolidified zinc base casting.

The preferred drawing die alloy composition may be obtained by meltingsubstantially pure zinc and, after elevating the temperature of themolten zinc to between about 950 F. and 1075 F., dissolving therein theappropriate amount of aluminum. This addition of aluminum retardsdrossing of the zinc at higher temperatures arid, if a cast iron meltingpot is employed, it inhibits attack of the pot by the zinc-rich melt.After further raising the temperature of the melt to betweenapproximately 1100 F. and 1300 F., the copper-iron-zirconium-man r 4 thebath. When the magnesium is dissolved, the final alloy may be cast toshape in suitable molds.

Although the aluminum can be introduced into the melt either before orafter addition of the intermediate alloy, the above alloying sequencehas been found to be most satisfactory. Alternatively, a portion of thisaluminum may be added prior to the introduction of the intermediatealloy and the remaining aluminum added after this alloy addition.

As hereinbefore explained, it is desirable that theironzirconium-manganese alloy have a density which approximates that ofthe zinc-rich melt in order to prevent flotation or segregation of theiron-zirconium-manganese particles. The density of zinc at its meltingpoint is 6.92 grams per cc., and the addition of about 4% aluminum and3.25% copper changes the density of the resultant alloy to slightly over6.9 grams per cc. Therefore, in order to obtain proper distribution ofthe iron-zirconiummanganese particles, it is desirable to form theseparticles of an alloy having a specific gravity of about 6.5 to 7.5grams per cc. The density of iron-is 7.87 grams per cc. and the densityof manganese is 7.2 grams per cc., while the density of commerciallyavailable zirconium is about 6.5 grams per cc. Hence, we have found thatan ironzirconium-manganese alloy consisting essentially of 50% iron, 25%zirconium and 25% manganese provides excel lent results. Such an alloyhas a calculated density of about 7.43 grams per cc., which is slightlyhigher than the specific gravity of the aforementioned zinc-rich melt.

It will be noted, however, that the densities of zirconium and manganesepermit the reduction or substantial elimination of iron in the pre-alloyinsofar as the density requirement is concerned. For example, an alloyof 50% manganese and 50% zirconium has a calculated density ofapproximately 6.87 grams per cc. and is sulficiently dense so that theparticles thereof will not present a serious floatation problem. Hence,the present invention in its broader aspects is intended to encompassthe use of zirconium-manganese particles as well asironzirconium-manganese particles. Generally, however, it is muchpreferred to include iron in the pre-alloy since this reduces the costof the resultant material to an appreciable extent and conserves the useof relatively scarce manganese and zirconium. Thus, the pre-alloypreferably contains at least 30% iron, and the iron may constitute asmuch a's approximately 70% of the iron-zirconium-manganese alloy.

We prefer to have a ratio of zirconium to manganese in theiron-zirconium-manganese alloy of about 1 to 1, but an appreciablevariation in the relative amounts of these three constituents ispermissible. Thus we have found that the wear resistance of a zinc basealloy may be substantially improved with an iron-zirconium-manganesepre-alloy comprising approximately 20% to 35% zirconium, 20% to 35manganese and the balance iron. Such a pre-alloy produces particles ofoptimum size and density. In some instances, however, the pre-alloy maycontain as little as 15% or as much as 55% zirconium, and the manganesecontent likewise may vary from about 15% to 55%.

When the iron-zirconium-manganese pre-alloy is mixed with the moltencopper, usually at a temperature of 2200 F. to 2700 F., it is preferredto form an intermediate alloy containing approximately 55% to copper. Ifthis alloy has a copper content less than 55 it is difiicult to placethe copper-rich matrix of the copper-iron-zircomum-manganeseintermediate alloy in solution in the zincrich melt. Therefore, a copperbase alloy comprising about 3% to 20% zirconium, 3% to 20% manganese, 5%to 35 iron and the balance copper is appropriate for use in carrying outthe present invention. In order to provide a zinc base alloy withapproximately 0.5% to 4% iron-zirconium-manganese particles, theintermediate alloy normally constitutes about 1% to.9% of the finalalloy, depending on the compositionof the pre-alloy,

,af A r 4 although 3% to 6. 5% is preferredPWheri such an intermediatealloy is added to' a zinc-rich melt, it should introduce into the finalalloy approximately 0.2% to 2% iron, 0.15% to 1% zirconium and 0.15% to1% manganese in the form of iron-zirconium-manganese particles and about0.5% to 5% copper which is not combined with these particles.

Since the hard particles result principally from the combination ofzirconium and manganese and are formed during the preparation of thepre-alloy, the alloying procedure employed in forming the hardener is ofimportance in achieving optimum, results. Accordingly, theiron-zirconium-manganese pre-alloy may be compounded by melting togetherthe proper amounts of these elements, preferably ata temperature ofapproximately 2900 F. to 3100 F. Inasmuch as zirconium is a ratherreadily oxidizable and nitridable element, it is desirable to use aninert gas as the melting atmosphere. We have obtained most satisfactorymelting and high zirconium recovery using an induction furnace under anargon atmosphere.

It will be noted that it is necessary to form'particles ofmanganese-zirconium or iron-zirconium-manganese in order to obtain highwear and score resistance in accordance with the invention. Merelyadding the iron, zir conium and manganese separately to the zinc-richmelt, even if these constituents are introduced in the aforementionedpreferred proportions, does not form these hard particles or provide thenecessary wear resistance. It is the alloy of iron, zirconium andmanganese, rather than the individual elements, which contributes thedesirable properties of wear and score resistance to the final zinc basealloy.

Wear tests were conducted to compare zinc base alloys formed inaccordance with our invention withthe same material devoid ofiron-zirconium-manganese particles. Samples 1 /8 inch wide and 42 inchhigh were prepared from the cast zinc base alloys to be tested, and eachspecimen was machined at one edge to prepare a inch by 1 /8 inch rubbingsurface. The specimens were next successively locked in a fixture of aWear test machine and placed in contact with a rotating smoothsurfacedwheel of low carbon steel having a face width of one inch. Increasedwear resistance was measured by decreased weight loss in grams.

A wear test using this apparatus was conducted in which the specimenload was increased during a fivehour period from zero load andautomatically adjusted to produce a constant frictional load rather thana constant load normal to the wheel. This test included a ten minuterun-in period in which only the weight of the specimen being tested andits holder bore against the wheel, a period of 1% hours to load thespecimen to 500 pounds, a 30 minute period at500 pounds to establish thefrictional characteristics, and the balance of the five hours run withthis established value of friction maintained constant. After each testany loosely adher ing, deformed metal and burrs were removed from theWear test sample, and loss in weight values were used in comparing thewear resistance of the specimens.

At the end of the test period the zinc base alloy specimens formed froma zinc base alloy consisting essentially of 3.25% copper, 4% aluminum,0.1% magnesium and the balance zinc showed an average Weight loss of0.4764 gram. On the other hand, a zinc base die alloy specimen ofsimilar composition but containing the afore mentioned preferred amountsof the iron-zirconiummanganese particles lost an average of onlyapproximate- 1y 0.0248 gram. The results of this test show how greatlythe presence of dispersed particles of the hard iron-zirconium-manganesealloy'increases the wear resistance of zinc base alloys.

Although the final alloy formed has been described as particularlysuitable as a drawing die material, it also may be employed toconsiderable advantage in other 6 applications in which high wearresistance, good castabil ity, uniformity of properties throughout acast section, good machinability, and anti-score properties are esimportance. i

While we have set forthherein specific examples of zinc base alloyspossessing high wear resistance characteristics due to the presence ofhard particles of manganese-zirconium or iron-zirconium-manganese, it isnot intended to restrict the invention to any specific zinc base alloy.We believe that we are the firstto discover the value of adding theseparticles to zinc base alloys generally, and the invention is not to berestricted except as defined in the following claims. 3 i

We claim: i V

1. A zinc base alloy characterized by high wear recomprisingapproximately 30% to 70% iron, 15% to 55% zirconium and 15% to 55manganese.

3. A zinc base alloy characterized by high wear resistance consistingessentially of at least approximately zinc and about 1 to 3% ofiron-zirconiurn-manganese particles dispersed throughout the alloy, saidparticles comprising approximately 30% to 70% iron, 15 to 55% zirconiumand 15 to 55 manganese.

4. An alloy comprising approximately 2% to 5% aluminum, 0.5 to 5%copper, 0.5 to 4% hard particles of iron-zirconium-manganese alloyofwhich the zirconium and manganese each constitutes 15% to 55 and thebalance substantially all zinc.

5. A highly wear-resistant zinc base alloy consisting essentially ofabout 2% to 5% aluminum, 0.5% to 5% copper, 0.02% to 0.3% magnesium, 0.5to 4%. particles of iron-zirconium-manganese alloy and the balance zincplus incidental impurities, said particles comprising approximately 30%to 70% iron, 15 to 55% zirconium and 15 to 55% manganese.

6. A casting alloy consisting essentially of about 3% to 5% aluminum, 2%to 3.5% copper, 0.05% to. 0.2% magnesium, approximately 1% to 3% hardiron-zircomum-manganese particles, and the balance substantially allzinc and incidental impurities, said par-ticles comprising approximately30% to 70% iron, 15% to 55% zirconium and 15 to 55 manganese.

7. A zinc base alloy characterized by outstanding wear resistance andcomprising approximately 2% to 5% aluminum, 0.5 to 5% copper, 0.2% to 2%iron, 0.15% to 1% zirconium, 0.15 to 1% manganese and the balancesubstantially all zinc plus incidental impurities, a substantialproportion of said iron, zirconium and manganese being present in theform of particles of iron-zirconium-manganese dispersed throughout saidzinc base alloy.

'8. An alloy consisting essentially of about 3% to 5% aluminum, 2% to3.5% copper, 0.05% to 0.2% magnesium, 0.2% to 2% iron, 0.15% to 1%zirconium, 0.15% to 1% manganese and 87% to 93% zinc, a substantialproportion of said iron, zirconium and manganese being combined in theform of hard particles of iron-zirconium? manganese alloy.

9. A method of increasing the wear resistance of a zinc base alloy whichcomprises adding to a zinc-rich melt a pre-alloy constituting 0.5% to 4%of the final iron, and consisting essentially of about 30% to 70% iron,15 to 55 zirconium and 15% to 55% manganese.

10. In a method of preparing a highly wear-resistant zinc base alloy,the step which comprises adding to a zinc-rich melt a pre-alloy having anetwork of ironzirconium-manganese in a coppenrich matrix, said networkcomprising approximately 30% to 70% iron, to 55% zirconium and 15% to55% manganese, said pre-alloy being added in an amount sufficient tocause the said iron-zirconium-manganese to constitute approximately 0.5%to 4% of the final alloy.

11. In a process of forming a wear-resistant zinc base alloy, the stepwhich comprises dissolving in a zinc-rich melt a pre-alloy consistingessentially of about 5% to 35% iron, 3% to zirconium, 3% to 20%manganese and the balance substantially all copper, said prealloy beingadded in an amount sufficient to produce an iron-zirconium-manganesecontent in the final alloy of approximately 0.5 to 4%.

12. A process of forming a wear-resistant zinc base casting alloy whichconsists of melting commercially pure zinc, dissolving therein at atemperature of approximately 950 F. to 1075 F. a quantity of aluminumequal to 2% to 5% of the final alloy and a pre-alloy consistingessentially of about 55% to 90% copper, 5% to 35% iron, 3% to 20%zirconium and 3% to 20% manganese, said pre-alloy being added in anamount such that the sum of the iron, zirconium and manganese contentsthereof constitute approximately 0.5% to 4% of the final zinc basealloy, and thereafter fiuxing the melt to remove objectionable oxides.

13. A process of forming a wear-resistant zinc base casting alloy whichconsists of melting commercially pure zinc, dissolving therein at atemperature of approximately 950 F. to 1075" F. a quantity of aluminumequal to about 2% to 5% of the final alloy, raising the temperature ofthe resultant zinc-rich meltto between approximately 1100" F. and 1300F., thereafter adding to said melt a pre-alloy consisting of copper,iron, zi-rconium and manganese, the composition of said prealloy beingsuch that the final alloy contains 2% to 5% aluminum, 0.5% to 5% copper,0.2% to 2% iron, 0.15% to 1% zirconium and 0.15% to 1% manganese,lowering the temperature of the zinc-rich melt to about 900 F. to 950F., fiuxing said melt to remove objectionable oxides, and subsequentlydissolving in the melt an amount of magnesium equal to 0.02% to 0.3% ofthe final alloy.

14. A zinc base alloy characterized by high wear, resistance comprisingat least 85% zinc, minor proportions of aluminum and copper, andapproximately 0.5% to 4% hard iron-zirconium-manganese particlesgenerally uniformly dispersed throughout said alloy, said particlesconsisting essentially of about 15%.to zirconium, 15% to 55% manganeseand the balance substantially all 11'011.

15. A method of increasing the Wear resistance of a zinc base alloywhich comprises adding to a zinc-rich melt comprising at least 85 zinc apre-alloy containing an amount of zirconium-manganese effective to formin the resultant zinc base alloy, upon solidification thereof, about 0.5to 4% dispersed, hard particles having a specific gravity ofapproximately 6.5 to 7.5 grams per cubic centimeter and containing atleast 15 zirconium and at least 15% manganese.

16. A method of increasing the wear resistance of a zinc base alloywhich comprises adding to a zinc-rich melt a pre-alloy containingiron-zirconium-manganese which forms in the resultant zinc base alloy,upon solidification thereof, an amount of dispersed, hard particles ofiron-zirconium-manganese equal to approximately 0.5% to 4% of said zincbase alloy, said hard particles consisting essentially of about 30% toiron, 15 to 55% zirconium and 15% to 55% manganese.

References Cited in the file of this patent UNITED STATES PATENTS2,048,288 Pierce et a1. July 21, 1936 2,372,546 Bunn Mar. 27, 19452,504,935 Morris Apr. 18, 1950 2,641,540 Mohling et al. June 9, 19532,747,989 Kirkby et al. May 29, 1956 2,795,501 Kelly June 11, 1957FOREIGN PATENTS 296,780 Germany Mar. 13, 1915 OTHER REFERENCES Zirconiumand Zirconium Alloys (published by ASM), Cleveland, Ohio (1953), pages283-290 relied on.

entra.

KARL H; AXLINE UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No, 2,909,429

Robert F., Thomson et al.

October 20, 1959 It is hereby certified that error appears in theprinted specificationof the above numbered patent requiring cor rectionand that the said Letters Patent should read as cor rected below.

I Column 3, line 25 for "metal" read melt ---g column 6, line 7O for"iron" read alloy Signed and sealed this 16th day of August 1960:.

(SEAL) Attest:

ROBERT c. WATSON M tes ting Officer Commissioner of Patents

1. A ZINC BASE ALLOY CHARACTERIZED BY HIGH WEAR RESISTANCE COMPRISING ATLEAST 85% ZINC AND ABOUT 0.5% TO 4% DISPERSED, HARD PARTICLES OF ANALLOY CONTAINING AT LEAST 15% MANGANESE AND AT LEAST 15% ZIRCONIUM, SAIDPARTICLES HAVING A SPECIFIC GRAVITY OF ABOUT 6.5 TO 7.5 GRAMS PER CUBICCENTIMETER.